Carbonates in the Poza Rica field are mass-transport deposits formed
by gravity flow and suspension processes in a deepwater basinal setting
(as great as 1000 m) in front of a by-pass margin associated with the
shallow-water Tuxpan platform. Reefal and grain-rich debris formed on
the platform. The carbonate debris wedge extends more than 20 km into
the basin.

The internal architecture of the debris wedge shows an orderly pattern
of depositional units that reflects control of relative sea-level changes
on availability of source material. Debris and mud flows composed of platform
and slope carbonate mud, sand, and clasts were generally deposited during
sea-level lowstands and transgressions or during early highstands when
the platform was rapidly aggrading, whereas hyperconcentrated to concentrated
density-flow and turbidite deposits composed of carbonate sand and lesser
mud were generally deposited when the platform was flooded and shedding
during highstands of sea level. The lower section of the debris wedge
is predominately debris- and mud-flow deposits totaling more than 300
ft thick, whereas the middle to upper section is composed mainly of hyperconcentrated
to concentrated density-flow deposits totaling more than 300 ft thick.
The uppermost section changes from debris flows updip to hyperconcentrated
to concentrated density flows downdip.

The field is approximately 30 km long and 5 km wide, covering an area
of 150 km2. With ~5 billion barrels of original oil in place, it is the
largest deepwater carbonate gravity-flow reservoir in the world. The major
reservoir rocks are grainstones, grain-dominated packstones, and grain-dominated
matrix breccias.